How to determine the cooling capacity of air conditioning or heat pump equipment

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RATED COOLING CAPACITY – How to Determine Air Conditioning or Heat Pump Equipment Rated Cooling Capacity

Explanation of a ton of cooling capacity (C) Carson Dunlop AssociatesThe cooling capacity of an air conditioning system is expressed in BTU’s or tons. One ton of cooling capacity equals 12,000 BTU’s/hour of cooling capacity.

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“One ton” of cooling capacity, historically, referred to the cooling capacity of a ton of ice. Tons of ice does not explain a key ingredient in the comfort produced by air conditioning systems, dehumidification of indoor air – that is, taking water out of the air.

Cool air can hold less water (in the form of water molecules or gaseous form of H2O) than warm air. Think of the warmer air as having more space between the gas molecules for the water molecules to remain suspended.

When we cool the air, we in effect are squeezing the water molecules out of the air. When an air conditioner blows warm humid building air across an evaporator coil in the air handler unit, it is not only cooling the air, it’s squeezing out some of the water in that air. Both of these effects, cooler air and drier air, increase the comfort for building occupants. Sketch courtesy of Carson Dunlop Associates.

There are several ways to determine the rated cooling capacity of an air conditioning system’s equipment:

Air Conditioning Equipment Age and Capacity from Equipment Numbers

Sketch on estimating the size or capacity of an air conditioner (C) Carson Dunlop AssociatesSerial number formats vary by range of years over which equipment was manufactured, and may vary among countries of manufacture for a given company’s equipment, for example between the U.S. and Canada for Carrier air conditioning equipment.

Example: a Carrier Compressor/Condenser Serial# 1389E54894 on a compressor unit.

Air conditioning equipment age from serial number for the example above, the equipment was made after 1980. The first four digits of the serial number are week and year of manufacture, in this case, week 13 of 1989.

See AIR CONDITIONER BTU CHART for a guide to selecting an air conditioning system with the proper cooling capacity in tons or in BTUs.

Sketch courtesy of Carson Dunlop Associates.

FROM MODEL # – Air conditioning equipment capacity from model number

Example: Carrier A/C Compressor Condenser Model# 38XD12400 (same unit as used for the serial number example above), there is variation in how Carrier assigned these numbers but typically the numbers indicate either tonnage or MBTUH. This example has digits in the 4th and 5th positions (right hand 5 digits), so the rating is in MBTUH for this number and “24” signifies 24 MBTUH or 2 tons of capacity.

Be sure to review our article on how to read the data in
for a guide to reading the system cooling capacity either directly off of the sticker on the equipment, or for examples of how to find them model number which can be …


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